Instances of criminal tampering with gelatinous capsules to alter their contents have alarmed the public in the past. Manufacturers have responded by providing improved packaging so that any tampering with the box or bottle containing the capsules is evident to the user. A further protection to the consumer can be provided by bonding the exterior of each capsule in a manner such that it can not be opened without visibly damaging the capsule.
Medicinal capsules are typically produced by filling a small dissolvable, gelatinous, U-shaped body with medicinal powder and then placing another similar gelatinous cap of larger diameter over the open end of the filled body to close the capsule. Capsules made in this manner are easily opened. The criteria for developing a tamperproof medicinal capsule are guided by the end use of the product. The product is taken orally. A typical patient's favorable reaction to the appearance of the capsule and avoidance of any discomfort to the patient in swallowing the capsule are significant factors in marketing the product.
Several methods have been used or studied for producing tamperproof capsules. Typical methods have included heat sealing, microwave sealing, and conventional industrial-type ultrasonic welding, which have limitations in the product quality or manufacturing efficiency. Heat sealing of the capsule cap and body is accomplished with an external heating element that produces a local brand-like distortion and discoloration. Microwave sealing does not leave a brand mark but produces undesirable discoloration and reduction in moisture content. To compensate for discoloration, a change in gel formulation for the capsule is required.
Ultrasonic welding is based upon interfacial or internal absorption of energy. Conventional commercial-type ultrasonic welders have been evaluated in which the ultrasonic motion of the tip of the welding tool is in the radial direction of the capsule. The weld produced is a short bar-shaped impression on one side of the capsule. Capsules have very thin walls and the finished capsule feels soft to the touch. Thus, the conventional ultrasonic welding mode is not efficient because it depends on capsule wall flexing caused ultrasonically and other losses at the tip of the welding horn to produce the weld. This method requires higher amplitudes of vibration and higher power into the welding transducer than should be necessary and results in a greater number of damaged capsules than are acceptable (a damage rate of 0.5 percent is typically the highest that is acceptable in the industry). Furthermore, the conventional ultrasonic welding method cannot accommodate the typical variations in capsule dimensions wherein some capsule walls are thicker than normal and others are thinner than normal. Also, typical production variations in the diameter of the cap and body are sufficiently large that conventional ultrasonic welding can result in distortion of the capsule, which is objectionable.
A variation of conventional ultrasonic welding involves rotation of the capsule to provide a circumferential weld, as in Japanese Pat. No. 833, January 1965. For conventional ultrasonic welding, the movement of the welding tip is in a plane perpendicular to the capsule axis. If the cap has the same diameter as the body and they are axially aligned and held together by suction on the outer side walls, a butt-type welding joint can be achieved by applying axial ultrasonic motion and axial compression forces between the cap and body as suggested by Japanese Pat. No. 59021, April 1983.
Alternatively, as disclosed in U.S. Pat. No. 4,325,761, Pace, the U-shaped cap can be produced with an interior circumferential shoulder against which the open end of the U-shaped body is pressed (axial compression) while applying ultrasonic motion in an axial direction to produce an internal circumferential butt weld. The methods of conventional ultrasonic welding described in the prior art are inefficient; they also produce poor welds and an unacceptable number of damaged capsules or require complex capsule holding devices or expensive special modification of the capsule cap design to achieve butt-type welds.